Loader coupler with visual locking indicator

The invention generally relates to couplings of the type used to mount detachable farm or construction implements on the free end of the arms of a prime mover vehicle such as a tractor, loader, or the like.

Loaders are powered vehicles running on wheels or tracks having hydraulically operated upper and lower pairs of arms extending from the front of the vehicle. Loader machines such as front-end loaders and tractor-loaders (each of which is sometimes referred to herein generally as a “loader”) often include a quick coupler operatively connected to the arms. The coupler is adapted to mate selectively and releasably with an implement for performing work, such as a construction attachment or agricultural attachment (e.g., a bucket, a boom, a fork attachment, a rake, or the like). Such coupler systems typically use a male master mounted on the upper and lower arms of the loader together with female coupler attachments affixed to an implement. The implement typically consists of a pair of upper hooks and lower protruding lugs. The upper hooks receive a generally horizontal male member on the coupler. The lower protruding lugs have slots or openings which are configured to receive movable locking wedges or pins combined with the coupler (as used herein “locking pins” shall include locking wedges and other suitably shaped locking members). The implement is secured or released by extension or retraction of hydraulically or manually actuated locking pins through the protruding lugs. To be properly connected, both upper hooks need to be fully around the upper horizontal bar member of the coupler and both locking pins need to be extended through the respective implement lugs of the implement. The coupler allows an operator of the loader to engage with and disengage from various implements as needed without exiting the operator's cab. Such couplers provide for improved machine productivity and operator convenience as compared conventional loaders that require the operator to exit the cab to connect and disconnect each implement. An exemplary coupler is disclosed in U.S. Pat. No. 4,708,579 (Baird et al.) issued on Nov. 24, 1987, the complete disclosure is hereby incorporated by this reference.

Prior couplers of the above type are disadvantageous in that there are no means of signaling the operator whether the locking pins are fully latched to the implement. In some cases, the coupling may approach the implement but, for one reason or another, the locking pins may not move fully into latching engagement with the implement. For example, the lug on the implement may be dirty or bent and therefore incapable of fully receiving the coupler's pin. Further, even if fully extended, the lug/pin engagement may occur at a location that is difficult for the operator to see from the cab. Accordingly, the operator must leave the prime mover vehicle and visually inspect the pins to make certain that the implement is securely attached. Still further, it is important to ensure the implement remains properly attached to the coupler during use. Damage to hydraulic lines, valves, and motors, leaking hydraulic fluid, and external forces acting on the locking pins during operation can all cause the locking pins to retract from an extended position to an unsafe position without warning to the operator.

There is therefore a need for an improved coupler which overcomes these and other drawbacks in the prior art.

One aspect of the present disclosure relates to a coupler assembly for coupling an implement to a prime mover vehicle. The coupler assembly includes a hydraulic system having a first fluid flow path and a second fluid flow path. The hydraulic system is configured to convey fluid under system pressure to a hydraulic cylinder for moving one or more locking pins between an extended position and a retracted position. A proximity sensor is in communication with the hydraulic system, the proximity sensor having an open position wherein system pressure is allowed to flow through the first fluid flow path toward the hydraulic cylinder and a closed position wherein fluid is prevented from flowing through the first fluid flow path toward the hydraulic cylinder. An indicator in communication with the hydraulic system through a third fluid flow path, the indicator is configured to indicate a first sign when system pressure is not received through the third fluid flow path and a second sign when system pressure is received through the third fluid flow path. The first sign is indicative of the locking pins not being in the extended position and the second sign is indicative of the locking pins being in the extended position.

Another aspect of the present disclosure relates to a coupler assembly configured to selectively couple a work implement to a prime mover vehicle. The coupler assembly includes a hydraulic system configured to convey hydraulic fluid under system pressure from a hydraulic motor or other source to move one or more locking pins between an extended position where the locking pins are received by openings or lugs in the work implement to secure the coupler assembly to the implement, and a retracted position wherein the locking pins are retracted from the openings or lugs to allow the implement to be removed from the coupler assembly. The hydraulic system of the coupler assembly is configured to be combined with and operated by the hydraulic system of a prime mover vehicle. In some embodiments the locking pins are the rod of a hydraulic cylinder. In other embodiments the locking pins are actuated by the rod of a hydraulic cylinder. The coupler assembly further includes one or more proximity sensors configured to determine whether the implement is seated properly with the coupler assembly. The proximity sensors are in communication with the coupler's hydraulic system and only allow the flow of hydraulic fluid through the system toward the locking pins when the implement is determined to be properly seated with the coupler. The coupler assembly further includes an indicator in communication with the coupler's hydraulic system. The indicator may be a visual indicator configured to visually indicate a first sign and a second sign. The first sign is indicative of the implement not being properly attached to the coupler and the second sign is indicative of the implement being properly attached to the coupler. In some embodiments the indicator physically moves between a first position to indicate the first sign and a second position to indicate the second sign, and is biased in the first position by a biasing member such as a spring. The indicator is biased in the first position and is only moved to the second position if certain conditions are met. In some embodiments, in order for the indicator to be moved to the second position signaling a proper attachment, the proximity sensor(s) must be actuated to allow fluid to flow through the hydraulic system to the locking pins and the locking pins must be fully extended. In some embodiment, if these conditions are met, then hydraulic fluid is conveyed through a fluid flow path to the indicator at a high enough system pressure to overcome the biasing force keeping the indicator in the first position, thereby moving the indicator to the second position. In other embodiments other conditions are also required to convey enough hydraulic pressure to move the indicator to the second position.

Another aspect of the present disclosure relates to a hydraulic system associated with a coupler assembly configured to selectively attach to a work implement. The hydraulic system associated with a coupler assembly is configured to be combined with and operated by the hydraulic system of a prime mover vehicle. The hydraulic system of the coupler assembly is configured to convey system pressure from the hydraulic system of a prime mover vehicle to move one or more locking pins between an extended position where the locking pins are received by openings or lugs in the work implement to secure the coupler assembly to the implement, and a retracted position wherein the locking pins are retracted from the openings or lugs to allow the implement to be removed from the coupler assembly. The hydraulic system of the coupler assembly includes one or more proximity sensors configured to determine whether the implement is seated properly with the coupler assembly. The proximity sensors are in communication with the coupler's hydraulic system and only allow the flow of hydraulic fluid through the system toward the locking pins when the implement is determined to be properly seated with the coupler. Each proximity sensor includes a permissive control valve that, in some embodiments, is plunger operated such that the implement provides force against the plunger when the implement is properly seated against the coupler. The permissive control valve is biased in a first position wherein fluid is not allowed to move through the hydraulic system toward the one or more locking pins. The force from the properly seated implement actuates the plunger to move the permissive control valve into a second position where hydraulic fluid is allowed to move in the hydraulic system toward the one or more locking pins. The hydraulic system of the coupler assembly further includes a fluid pathway from the one or more locking pins to an indicator, which may be a visual indicator, configured to move between a first position having a first sign or signal and a second position having a second sign or signal. The first position is indicative of the implement not being properly attached to the coupler and the second position is indicative of the implement being properly attached to the coupler. The indicator is biased in the first position by a biasing member such as a spring and is only moved to the second position if certain conditions are met which allow hydraulic system pressure to overcome the biasing force thereby moving the indicator to the second position indicating proper attachment with the implement. In some embodiments, in order for the indicator to be moved to the second position signaling a proper attachment, the proximity sensors must be actuated to allow fluid to flow through the hydraulic system to the locking pins and the locking pins must be extended, which opens a fluid pathway allowing system pressure to flow to the indicator. In other embodiments other conditions are also required to provide enough hydraulic pressure to move the indicator to the second position.

Another aspect of the present disclosure relates to a method for determining a state of a coupler assembly. The method includes providing a coupler assembly having a hydraulic system, as described above, the coupler assembly configured to be selectively attached to an implement. Connecting the hydraulic system of the coupler to the hydraulic system of the prime mover vehicle and attempting to attach the implement to the coupler. Actuating system pressure to move the locking pins to the extended position. In the event the implement is properly seated with the coupler, the proximity sensors allowing fluid to flow through the hydraulic system toward the locking pins thereby meeting a first condition. In the event the implement is not properly seated with the coupler, the proximity sensors preventing fluid from flowing through the hydraulic system toward the locking pins and the indicator remaining in the first position without meeting the first condition. Upon meeting the first condition, fluid pressure is conveyed through the system to extend the locking pins to the extended position. In the event the locking pins extend to the extended position, a second condition is met and hydraulic system pressure overcomes the biasing force keeping the indicator in the first position thereby moving the indicator to the second position indicating the implement has been properly attached to the coupler assembly. In the event the locking pins do not extend to the extended position, the second condition is not met and the indicator remains in the first position. Actuating system pressure to move the locking pins to the retracted position thereby causing the biasing force of the indicator to be greater than retraction system pressure so the indicator returns to the first position.

The invention generally relates to a coupler assemblyhaving a hydraulic systemconfigured to actuate an indicatorupon the occurrence of certain conditions. The hydraulic systemof the coupler assemblyis configured to be fluidly connected to and operated by the hydraulic system of a prime mover vehicle. The hydraulic systemof the coupler assemblyis configured to convey a fluid, which may be a hydraulic fluid, from the hydraulic system of the prime mover vehicleto a hydraulic cylinderand other system components described herein. The fluid is conveyed into the hydraulic systemof the coupler assemblyunder system pressure and is conveyed back to the hydraulic system of the prime mover vehicleunder return system pressure. The hydraulic system described herein will primarily relate to the hydraulic systemof the coupler assembly. Further, reference is primarily made to “hydraulic” fluid, however, any other suitable fluid may be used with the system.

generally show the coupler assemblyattached to the armsof a prime mover vehicle.shows the coupler assemblyfurther attached to an implement. As shown, the implementis a bucket, however, any suitable implementmay be attached to the coupler assembly.

show the general components of the coupler assembly. The coupler assemblyincludes components configured to selectively attach to a prime moverand to an implement. The components of the coupler assemblyconfigured to selectively attach to the implementinclude an upper generally horizontal memberconfigured to be received by the hooksof an implement. The components may also include one or more locking pins, which may be the rod of one or more hydraulic or pneumatic cylinders, configured to be received by the openings or lugsof an implement. In some embodiments the locking pinsare operatively connected to the rods of one or more cylindersso that the locking pinsare considered an extension of the rods.

The coupler assemblyfurther includes a hydraulic systemconfigured to move the one or more locking pinsbetween an extended position where the locking pinsare received by the openings or lugsin the work implementto secure the couplerto the implement, and a retracted position wherein the locking pinsare retracted from the openings or lugsto allow the implementto be removed from the coupler. In the embodiments shown in, the locking pinsare the rod of one or more hydraulic cylindersand the terms “locking pins” and “rod” are both sometimes shown and described with reference number. In embodiments where more than one locking pinis used to secure the implementto the coupler, each locking pinmay comprise a separate hydraulic cylinder. In other embodiments, like the embodiments shown in, a double acting double rod cylinderhaving a first pistonand rodconfigured to extend outward in a first direction to engage a first lugand a second pistonand rodare configured to extend outward in a second direction to engage a second lug. In still other embodiments a standard double acting cylinderhaving only one rodmay be used. In these embodiments the cylinderhas only one pressure tap to line P. The second locking pincould be attached to the opposing end of the cylinder'shousing. In some embodiments the locking pinsmay be actuated by a hydraulic cylinder, but the locking pinsare separate from the components of the cylinder.

The coupler assembly further includes one or more proximity sensorsconfigured to determine whether the implementis in a seated position or a non-seated position relative to the coupler. Positioning the implementwith the coupler assemblyin the seated position may include ensuring the implementis within a predetermined distance from a predetermined area of the coupler assembly. It may also include ensuring the implementaligns with the coupler assemblyat a predetermined angle. It may also include ensuring the rear face of the implementis aligned in planer parallel with the front face of the coupler assembly. In some embodiments proper seating will not occur unless all of the hookson the implement properly engaged the cross horizontal memberon the coupler assembly. As described below in more detail, the proximity sensorsare in communication with the coupler assembly'shydraulic systemand only allow the flow of hydraulic fluid through the system toward the locking pinswhen the implementis determined to be properly seated with the coupler. Each proximity sensorincludes a permissive control valvehaving an open position and a closed position. In the open position hydraulic fluid is allowed to flow in a first direction toward the locking pinsand also in a second direction towards the hydraulic supply/reserve tank. In the closed position hydraulic fluid is prevented from flowing in the first direction toward the locking pins, but is still allowed to flow in the second direction toward the tank. The permissive control valveis biased in the closed position so that hydraulic fluid can only pass through toward the locking pinsif the proximity sensorsdetect that the implementis properly seated with the coupler assembly. In some embodiments, two proximity sensorsare in communication with the hydraulic systemin series so that both sensorsmust be in their open position in order for system pressure to flow toward the cylinder.

The proximity sensorshelp determine whether the implementis property seated against the coupler. The proximity sensorsmay detect the proper seating of the implementand operate the permissive control valvemechanically or electrically. In some embodiments the proximity sensorsoperate mechanically by physically actuating a plungerthat is movable between an extended position and a retracted position and is biased in the extended position. In the extended position the permissive control valveis in its closed position wherein a check valveprevents hydraulic fluid from flowing into the system (toward the locking pins), but still allows fluid to flow out of the system toward the tank. In the retracted position the permissive control valveis in its open position allowing fluid to flow both into the system toward the locking pinsand out of the system toward tank. In use, the implementprovides force against the plungerwhen property seated against the coupler assemblyto move the plungerto the retracted position. Movement of the plungerto the retracted position opens the permissive control valveto allow hydraulic fluid to flow toward the cylinderfor moving the locking pinsto the extended position. In other embodiments electrical components may determine proper seating and open the permissive control valveto allow hydraulic fluid to flow toward the locking pins.

As generally described above, in some embodiments the plungeris positioned to physically engage a portion of the implementwhen the implement is properly seated against the coupler assembly. In some embodiments, the plungeris positioned to extend outward from the front portion of the coupler assemblyso that a rearward portion of the implementengages the plungerwhen property seated against the face of the coupler assembly. Multiple plungersmay be positioned at different locations on the coupler assemblyto help ensure multiple portions of the implementare property seated with the coupler assembly.show exemplary locations where the plungermay be positioned on the coupler assembly.shows reference for the section views shown in. In, two plungersare positioned to be actuated by the rearwardly protruding lugsof the implementas the two components,engage each other. The plungersmay be positioned behind the front face of the coupler assemblysince the lugsare typically received by openingsin the front face when properly seated. After the implement's hookshave been positioned on coupler's upper members, the lower portion of the implementis rotated backwards toward the coupler assemblyand the lugsactuate the plungerif the position and alignment of the coupler assemblyand implementis correct. In, two plungersare positioned to extend outward from opposing lower lateral surfaces of the front face of the coupler assembly. The lower lateral surfaces may be pads or rests on the front face of the coupler assemblyconfigured to receive or cushion corresponding lower portions of the implementas the implementis rotated backwards toward the coupler assembly.

The coupler assemblyfurther includes an indicatorin communication with the coupler assembly's hydraulic system. In some embodiments the indicatoris configured to visually indicate a first signto the operator and a second signto the operator. The first signis indicative of the implementnot being properly attached to the coupler assemblyand the second signis indicative of the implementbeing properly attached to the coupler assembly. In some embodiments the indicatoris a visual indicator which provides an electronic sign or signal, such as a colored light or textual message, to communicate the first signand the second sign. In some embodiments the indicatoris a visual indicator which is member such as a flag, bladder, balloon, or pin which physically moves between a first position to indicate the first signand a second position to indicate the second sign. The member may have colors or shapes which help the operator identify whether the indicator is communicating the first signor the second sign. In embodiments where the indicatoris a bladder or balloon, when the predetermined conditions are met for a proper connection between the couplerand the implement, hydraulic fluid flows into the bladder or balloon causing movement or inflation that is visible to the operator. In some embodiments the indicatoris an audio indicator configured to provide a noise to indicate a first signand/or the second signto the operator. In some embodiments the indicatoris configured to provide other sensory stimuli to the operator to indicate a first signand/or the second sign, such as a vibrating steering wheel, seat, or joystick.

Inthe indicatoris retracted in the first position to indicate the first sign. The indicatoris biased in the first position and is only moved to the second position if certain conditions are met. In order for the indicatorto be moved to the second position signaling a proper attachment, the proximity sensorsmust be actuated to satisfy a first condition to allow fluid to flow through the hydraulic systemtoward the locking pinsand the locking pinsmust be extended to satisfy a second condition to engage the lugs. The engagement of the locking pinsand lugsis not sensed directly, but the indicatorcan determine whether the locking pinshave been extended beyond a predetermined position by the amount of hydraulic system pressure it receives through line P. A predetermined amount of system pressure is required to overcome the biasing force to move the indicatorto the second position. In some embodiments, if the first condition and the second condition are met, then hydraulic fluid flows through a fluid flow path Pto the indicatorto move the indicatorto the second position by hydraulic pressure. In these embodiments, the indicatoris biased in the first position by a biasing member, such as a spring. The pressure through fluid flow path Pmust be greater than the biasing force of the biasing memberin order to move the indicatorto the second position. As described below in more detail, there are many conditions wherein the operator may think there is a proper attachment between the implementand the coupler, but the attachment is actually improper or unsafe. In these unsafe instances the system is configured to convey less hydraulic pressure to the indicatorthan necessary to overcome the biasing force, thereby positioning the indicatorin its first position. In some embodiments other conditions are also required to convey enough hydraulic pressure to move the indicatorto the second position.

are section views showing the locking pinsin the retracted position () and extended position (). As noted above and as shown in, in the extended position, the locking pinsengage the lugsof the implement.

show the operation of the hydraulic systemof the coupler assemblyunder different conditions. These figures and their accompanying description provide further disclosure about the features described above. The figures show the same hydraulic systemunder different conditions. A condition or feature described with respect to one of the figures is applicable to the other figures if the system is under the same conditions. The figures show portions of an exemplary hydraulic system for a prime mover vehicle, however, the hydraulic system described herein will primarily relate only to the hydraulic systemof the coupler assembly.

Generally,show the hydraulic systemhaving two proximity sensors, each with permissive control valvesactuated by plungers, as described above. Line Preceives system pressure from the hydraulic pumpwhen the operator activates the extension of the locking pins. Conversely, line Preceives system pressure from the hydraulic pumpwhen the operator activates the retraction of the locking pins. In the illustrated embodiment, the system pressure is controlled on the machine side by switchesA andB, however, any other suitable actuation control means may be used. The coupler's hydraulic systemincludes a pilot operated check in both line Pand line P. The pilot operated check comprises a check valve,in each line P, P, respectively, which requires the operator to activate a switchA,B in order for pressure to flow out of the system (away from the cylinder). This helps to prevent the locking pinsfrom moving without operator input. For example, if an implementis attached to the coupler assemblyand the system loses pressure due to the hydraulic lines P, Pbecoming damaged or the pumpfailing, the check valves,will prevent fluid from moving away from the cylinderthereby keeping the locking pinslocked in place to help ensure the implementdoes not inadvertently detach from the coupler assembly.

To relieve pressure from the cylinderand unlock the position of the locking pins, pilot lines,when pressurized, convey pressure to unseat the check valve,on the return pressure (vent) side of the system allowing fluid to return to the tank. Fluid only passes through pilot lines,when the operator actuates either extension or retraction to unseat the check valve,on the opposite (return pressure) hydraulic line P, P. The pilot lines,will not unseat the check valves,without action by the operator. System pressure through line Pextends the locking pinsoutward toward the extended position (if the proper conditions described herein are met). Line Pconnects the hydraulic cylinderand the indicator. Line Pis in fluid communication with the hydraulic cylinderthrough junction portsso that system pressure through line Penters line Ponly after the locking pinshave moved to their extended position. Once the pistonsof each locking pinextend past their respective junction ports(from a first side of the junction portto a second side of the junction port) to line P, then system pressure travels through line Pand moves the indicatoragainst the biasing force provided by the biasing memberfrom the first position showing the first signto the second position showing the second sign. The indicatormoves to indicate the second signbecause the hydraulic system pressure through line Pis greater than the biasing force acting on the indicator.

A pressure relief valvehelps to ensure the indicatordoes not remain in the second position (continue to show the second sign) during retraction when system pressure is introduced into line Pand line Pis vented to tank. The pressure relief valvehas an open position and a closed position and is biased in the closed position. In the open position, the pressure relief valveallows fluid to pass from line Pto line Palong line, then back to tank. The pressure necessary to overcome the biasing force and move the pressure relief valveto the open position is less than the pressure necessary to move/keep the indicatorin the second position. Therefore, when Pis pressurized and Pis vented, pressure in Pnever reaches full system pressure, but is relieved at the relief set point pressure of relief valve, which, in turn, keeps Ppressure less than needed to move the indicatorto the second position.

shows a condition where the implementis attached to the coupleror an implementis improperly seated against the coupler. The operator has activated the extension of the locking pins. The proximity sensorsare in their extended/non-actuated/closed state thereby preventing hydraulic fluid from flowing through the permissive control valvetoward the locking pins. The indicatoris in the first position since it is not receiving system pressure, indicating the implementis not properly attached to the coupler. Note, the embodiment shown includes two proximity sensorspositioned at different locations on the coupler, however, any number may be used. The proximity sensorsshows are combined with the coupler assembly'shydraulic systemin series so that both sensorsmust be in their open position in order for system pressure to flow toward the cylinder.

shows a condition where the operator has activated the extension of the locking pinsand one of the proximity sensorshas been actuated to open the permissive control valve, but the second proximity sensorhas not been actuated thereby preventing hydraulic fluid from flowing through the second permissive control valvetoward the locking pins. This condition indicates that the implementis improperly seated or misaligned on the coupler. In this embodiment both of the proximity sensorsmust by actuated to allow fluid to flow through the permissive control valvetoward the locking pins. The indicatorremains biased in the first position since it is not receiving system pressure, indicating the implementis not properly attached to the coupler.

shows a condition where the locking pinsare extending, but have not yet reached their fully extended position, the implementis properly seated against the coupler, as indicated by the proximity sensorshaving been actuated to allow fluid to pass through the permissive control valvestoward the locking pinsvia line P. As the locking pinsmove toward extension, hydraulic fluid is flowing toward the hydraulic cylinderthrough line Pwhere the fluid enters the cylinderon the piston side. Hydraulic fluid is venting from the rodside of the cylindertoward the tankthrough line Pas the locking pinsextend. The indicatoris in the first position indicating the implementis not properly attached to the couplersince the pinshave not yet fully extended and the indicatoris not yet receiving system pressure. The rod side of the cylinderis in fluid communication with line P, however, the rod side pressure, which is the return pressure (vent) in communication with the tank, is not enough to move the indicatorto the second position. As explained elsewhere herein, each of the primary lines Pand Pcontain a pilot operated check comprising check valve,, respectively, to help maintain system pressure to the locking pinsand to the indicatorwhen the control switchesA,B are moved to neutral after the locking pinshave been fully extended. When hydraulic fluid is being pumped through the system in either the forward or reverse direction, one of the check valves,is unseated to allow fluid to flow back to tank. For example, during extension, fluid flows from the pumpthrough line Ptoward the hydraulic cylinder. A small amount of hydraulic fluid passes through pilot lineto unseat check valve, thereby allowing return/vented fluid to flow from rodside of the hydraulic cylindertoward the tankthrough line P. During retraction of the locking pins, fluid flow from the pumpthrough line Ptoward the hydraulic cylinder. A small amount of hydraulic fluid passes through pilot lineto unseat check valve, thereby allowing fluid to flow from the hydraulic cylindertoward the tankthrough line P.

shows a condition where the implementis properly seated against the coupler, as indicated by the proximity sensorswhich have been actuated to allow fluid to pass through the permissive control valvestoward the locking pinsand the operator has activated the extension of the locking pins. In this condition, hydraulic fluid began to flow toward the hydraulic cylinderthrough line P, but both of the locking pinsstalled short of full extension. The indicatoris in the first position indicating the implementis not properly attached to the coupler. Since the pinshave not yet fully extended, system pressure is not received by the indicatorthrough line P, so the biasing force of the biasing memberholds the indicatorin the first position. In some embodiments, in order for line Pto receive system pressure, the cylinder'srodsneed to be at full stroke or nearly at full stroke before junction portsare exposed to system pressure and the indicatoris properly actuated.

shows a condition where one of the locking pinsis fully extended and the other locking pinstalled short of full extension. The implementis properly seated against the coupler, as indicated by the proximity sensorswhich have been actuated to allow fluid to pass through the permissive control valvestoward the locking pins. Hydraulic fluid is flowing toward the hydraulic cylinderthrough line Pand hydraulic fluid is flowing from the cylindertoward the tankthrough line Pas the locking pinsextend. One extended locking pinhas moved far enough to allow system pressure to pass through one of the junction portsinto line Ptoward the indicator. However, the other locking pinwhich has not fully extended provides a fluid pathway through its respective junction portfor the system pressure in line Pto move back to tank through line P. The amount of pressure necessary to overcome the biasing force and activate the indicatoris more than the system return pressure to tank. Therefore, the indicatorremains is in the first position indicating the implementis not properly attached to the couplersince the locking pinshave not yet fully extended. In other embodiments (not shown), each locking pinmay be fluidly connected to its own indicator.

shows a condition where the coupler assemblyhas successfully aligned with and locked to the implement. The implementis properly seated against the couplerand the locking pinshave both fully extended. During extension hydraulic fluid system pressure flows toward the hydraulic cylinderthrough line Pand hydraulic fluid return pressure (vent) flows from the cylindertoward the tankthrough line P. Both of the locking pinshave fully extended thereby allowing hydraulic fluid system pressure to enter line Pfrom the piston side of both pins. Line Pis in fluid communication with the hydraulic cylinderthrough junction portspositioned where line Preceives system pressure from line Ponly after the pistonhas been extended to a predetermined position that is far enough for the locking pin/rodto extend through the opening in the lug. The system pressure through line Pis greater than the biasing force acting on the indicator, thereby moving the indicatorto the second position indicating the implementis properly attached to the coupler. In this illustration, two conditions are met to allow system pressure to reach the indicator. Namely, the implementis properly seated and the locking pinsare fully extended.

shows a condition where the operator has moved one or both of the switchesA,B to neutral so the hydraulic motoris no longer pumping fluid through the hydraulic system. The implementis properly seated against the coupler assemblyand both of the locking pinshave fully extended thereby allowing hydraulic fluid to enter line Pand move the indicatorto the second position, indicating the implementis properly attached to the coupler. Check valvesandhold system pressure in the cylinderand in the indicator, thereby ensuring the locking pinsremain extended and the indicatorremains in the second position.

shows a condition where system pressure is leaking into the hydraulic systemthrough the retract side of the switch'sA,B valves and into line P. The pilot operated check system prevents the locking pinsfrom retracting because the leak pressure is not enough to unseat check valvethrough pilot line. A full (or nearly full) amount of system pressure is required through either line Por Pin order to provide enough pressure through the respective pilot line,to unseat the respective check valve,. The check valves,hold system pressure in the cylinderand indicatordespite the pressure leak.

shows a condition where an external force, indicated by the arrows A, is trying to force the locking pinsto retract when the control switchB is in neutral. The implementis properly seated against the couplerassembly and both of the locking pinshave fully extended thereby allowing hydraulic fluid to enter line Pand move the indicatorto the second position indicating the implementis properly attached to the coupler. The pilot operated check valvesandhold system pressure in the cylindereven if an external force A tries to push the locking pinsback to their retracted position.

shows a condition similar to the one shown in, however, inthe hoses Pand/or Pare damaged as indicated by the Xs. Pilot operated check valvesandhold system pressure thereby ensuring the locking pinsremain extended and the indicatorremains in the second position.

shows a condition where the operator has activated the retraction of the locking pinsso system pressure from the hydraulic motormoves through line Ptoward the rod side of the cylinder. As described above, some fluid passes through pilot linecausing check valveto become unseated so fluid from the piston side of the cylindercan be returned to tank. In this condition, the pistonshave not yet retracted past the junction ports. The indicatormoves to the first position since the system return pressure is less than the pressure required to hold the indicator in the second position.

shows a condition similar to, but in this condition the pistonshave retracted past the junction ports. After the locking pinsretract far enough that the pistonspass the junction ports, line Pcould be exposed to the system pressure causing the indicatorto falsely show the second sign. A pressure relief valvehelps to prevent this situation. The pressure necessary to actuate the pressure relief valveand allow system pressure to pass from line Pto line Pthrough lineis less than the pressure necessary to move/keep the indicator in the second position. In other words, anytime the rod side of the cylindersees full system pressure, the pressure relief valveis actuated causing some pressure from line Pto flow to tank, and the force of the biasing memberovercomes the partial system pressure in line Pthereby moving the indicatorto the first position.

shows a condition similar to, however, inthere is no implementattached to the coupler assembly. Since there is no implementattached, the permissive control valvein the proximity sensorsmove to their biased/closed position wherein they allow fluid to move toward the tank, but not toward the locking pins. The pressure relief valveallows fluid to pass from line Pto line Ptoward tankthrough linewithout moving the indicator to the second portionsince the pressure necessary to actuate the pressure reliving valveis less than the pressure necessary to move/keep the indicator in the second position. Pressure would continue through the pressure relief valveeven if the operator continued activating the retracts switchA,B.

Having thus described the invention in connection with the preferred embodiments thereof, it will be evident to those skilled in the art that various revisions can be made to the preferred embodiments described herein without departing from the spirit and scope of the invention. It is my intention, however, that all such revisions and modifications that are evident to those skilled in the art will be included with in the scope of the following claims.